Field of the Invention
The invention pertains to medicine and biology and deals with DNA-RNA hybrids endowed with immunotropic and antiviral activities, the method for the preparation thereof, a pharmaceutical preparation based on the DNA-RNA hybrid as well as preparations on the basis of DNA endowed with the antiviral (including anti-HIV) activity, and methods for the preparation thereof.
There is a known method of preparing the hybrid by mixing DNA and RNA solutions in formaldehyde under definite temperature conditions for analytical purposes. The resulting hybrid possesses no marked biological activity. Moreover, under conditions of a high formaldehyde concentration modification of DNA in primary amino groups may occur (1) which leads to the loss of the specific activity and mutagenicity.
At the present time there are known preparations on the basis of RNA, exogenous DNA as well as nucleotides. The preparation on the basis of RNA-sodium nucleinate is endowed with the leukostimulating and weak immunostimulating activity (2). The preparations based on exogenous DNA have the leukostimulating activity in cytopenia induced by cytostatic therapy (3). Some data are available on the use of nucleotides as antiviral preparations (4).
The limitations of the known preparations on the basis of nucleic acids consist in a narrow range of the pharmacological effect.
There are known methods of achieving the antiviral activity of DNA preparations by modification thereof by means of physico-chemical or chemical treatments.
Thus, there are known methods of DNA modification by complexes with salts of polyvalent metals (5) or EDTA (6). In such physico-chemical method of modification, DNA preparations with molecular weight 300,000-500,000 D are mixed with Fe, Ni, Co, Zn, Mn, Mg salts at a molar ratio of 10-1000:0.5-3.0 (5), or preparations of high molecular DNA are mixed with EDTA (6). The resulting products show the anti-AIDS effect, however, at the same time they have significant cytotoxicity.
There is a known method of enhancing the antiviral activity of DNA by transforming it into apurinic or apyrimidinic acid, that is, DNA derivatives devoid in the former instance of arurinic and in the latter instance of pyrimidinic bases (6).
In accordance with the method (6), arurinic acid is prepared from Na-DNA preparations by thermolysis in an acid medium at pH from 1.5 to 4.0. The resulting products are of oligomeric nature, their molecular weights not exceeding 15-19 kD. Moreover, DNA is known to denaturate under these conditions. Both factors have a negative effect on the biological activity of DNA.
According to the same method (6), apyrimidinic acid is obtained either by alkaline hydrolysis with 0.3 N KOH, or by hydrazinolysis of DNA preparations. It has been established, however, that under these conditions there occur not only denaturation and destruction of the long strand structure but also transformation of purines into derivatives thereof, most likely into hydrazones. Thus, the final compound partially loses purine bases, or purine bases are partially transformed into derivatives. Such compounds cannot be considered to be promising as medicinal preparations since, first, they contain mutations and, second, their composition is not homogeneous, that is, such compounds provide no stable and reproducible pharmacological effect.